1. Field of the Invention
The present invention relates to a laminated optical film, and a liquid crystal panel and a liquid crystal display apparatus using the laminated optical film. More specifically, the present invention relates to a laminated optical film having a polarizer and two optical compensation layers, and a liquid crystal panel and a liquid crystal display apparatus using the laminated optical film.
2. Description of Related Art
Various optical films each having a polarizing film and an optical compensation layer in combination are generally used in an image display apparatus (such as a liquid crystal display apparatus) so that optical compensation is performed.
In general, a circularly polarizing plate which is one type of the above-mentioned optical films can be produced by combining a polarizing film and a λ/4 plate. However, the λ/4 plate has characteristics providing larger retardation values with shorter wavelengths, so-called “positive wavelength dispersion characteristics”, and the λ/4 plate generally has high positive wavelength dispersion characteristics. Thus, the λ/4 plate has a problem in that the plate cannot exhibit desired optical characteristics (such as functions as the λ/4 plate) over a wide wavelength range. In order to avoid the problem, there has been, in recent years, proposed a retardation plate having wavelength dispersion characteristics providing larger retardation values with longer wavelengths, so-called “reverse dispersion characteristics”, such as a modified-cellulose-based film and a modified-polycarbonate-based film. However, those films have a problem with cost.
At present, the following method is employed: a λ/4 plate having positive wavelength dispersion characteristics is combined with a retardation plate providing larger retardation values with longer wavelengths or a λ/2 plate, to thereby correct the wavelength dispersion characteristics of the λ/4 plate (see Japanese Patent No. 3174367, for example). However, according to those technologies, the enhancement of a screen contrast and the reduction in a color shift are insufficient.